Internal combustion engines require valve actuation systems to control the flow of combustible components, typically fuel and air, to one or more combustion chambers during operation. Such systems control the motion and timing of intake and exhaust valves during engine operation. In a positive power mode, intake valves are opened to admit fuel and air into a cylinder for combustion and exhaust valves are subsequently opened to allow combustion products to escape the cylinder. This operation is typically called a “main event” operation of the valves.
In addition to positive power main event operation, valve actuation systems may be configured to facilitate “auxiliary events” during engine operation. These may include, but are not limited to, engine braking, exhaust gas recirculation (EGR) and internal exhaust gas recirculation (iEGR). During these auxiliary events, valve timing and motion may be controlled to cause the engine to recirculate exhaust gases to achieve improved emissions, or to cause the engine to absorb energy from the engine load in engine braking operations.
Valve movement during main event positive power modes of operation is typically controlled by one or more rotating cams as motion sources. Cam followers, push rods, rocker arms and other elements disposed in a valve train provide for direct transfer of motion from the cam surface to the valves. For auxiliary events, “lost motion” devices may be utilized in the valve train to facilitate auxiliary event valve movement. Lost motion devices refer to a class of technical solutions in which valve motion is modified compared to the motion that would otherwise occur as a result of actuation by a respective cam surface alone. Lost motion devices may include devices whose length, rigidity or compressibility is varied and controlled in order to facilitate the selective occurrence of auxiliary events in addition to, or as an alternative to, main event operation of valves. Lost motion devices may be viewed as a subclass of a larger category of variable length piston assemblies, which may have application beyond those involving lost motion.
Prior art lost motion systems typically rely upon hydraulic or pneumatic working fluids (i.e., oil or air) for their operation. As a result, such systems are not readily adaptable to engines that do not utilize such working fluids, or that use such fluids at relatively low pressures that aren't sufficient to actuate lost motion systems.
In addition to lost motion systems, prior art valve actuation systems may require variable length elements that may be actuated to provide other functions, such as braking action provided by bleeder brake components. Such variable length elements may be used to selectively actuate engine valves to cause a bleeder brake operation to occur.
With the use of mechanically interacting elements and surfaces, another challenge in the art is to provide actuating assemblies that can withstand the rapid and repeated cycling and stresses that occur in an engine valve train environment and which reduce the potential for excessive peak stresses to develop during operation.
It would therefore be advantageous to provide systems and methods that address the aforementioned shortcoming and others in the prior art.